Field of the Technology
An atom or group transfer radical polymerization process conducted in aqueous media in the presence of a low concentration of soluble transition metal catalyst wherein a well-controlled polymerization is augmented by the addition, or in situ formation, of an activator regenerator.
Description of the Background of the Technology
Since its discovery atom transfer radical polymerization (ATRP) has gained increasing attention because ATRP couples the advantages afforded by conventional free radical polymerization (RP) to (co)polymerize a wide range of monomers using various commercially viable processes, including bulk, solution and various bi-phasic processes, with the ability to synthesize polymeric materials with predetermined molecular weight (MW), low polydispersity (PDI), controlled composition, site specific functionality, selected chain topology and selectively incorporate bio- or inorganic species into the final product. ATRP employs a rapid and reversible catalytic activation of alkyl (pseudo)halides by a soluble metal complex in a low oxidation state, exemplified herein, but not limited to the most frequently employed transition metal CuI, to generate radicals and the transition metal complex in a higher oxidation state, CuII, which rapidly acts to deactivate the growing (co)polymer chain.
Matyjaszewski and coworkers disclosed the fundamental four component ATRP process comprising the addition, or in situ formation, of an initiator, in this case a molecule with a transferable atom or group that is completely incorporated into the final product, a transition metal and a ligand that form, a (partially) soluble transition metal complex that participates in a reversible redox reaction with the added initiator or a dormant polymer to form the active species to (co)polymerize radically polymerizable monomers. The basic ATRP procedure and a number of improvements to the basic ATRP process have been disclosed in a number of commonly assigned patents and patent applications: U.S. Pat. Nos. 5,763,546; 5,807,937; 5,789,487; 5,945,491; 6,111,022; 6,121,371; 6,124,411; 6,162,882; 6,624,262; 6,407,187; 6,512,060; 6,538,091; 6,541,580; 6,624,262; 6,627,314; 6,759,491; 6,790,919; 6,887,962; 7,019,082; 7,049,373; 7,064,166; 7,125,938; 7,157,530; 7,332,550; 7,407,995; 7,572,874; 7,678,869; 7,795,355; 7,825,199; 7,893,173; 7,893,174; 8,252,880; 8,273,823; 8,349,410; 8,367,051; 8,404,788; 8,445,610; U.S. Ser. Nos. 12/451,575; 12/921,296, 13/260,504; 13/390,470; 13/734,747; 13/993,521, 14/065,370; 14/239,181, 14/373,553 and 14/379,418 all of which are herein incorporated by reference in their entirety to provide background and definitions for the present disclosure.
ATRP has also been discussed in numerous publications with Matyjaszewski as co-author and reviewed in several book chapters. [Matyjaszewski, K. et al. ACS Symp. Ser. 1998, 685, 258-283; ACS Symp. Ser. 1998, 713, 96-112; ACS Symp. Ser. 2000, 729, 270-283; ACS Symp. Ser. 2000, 765, 52-71; ACS Symp. Ser. 2000, 768, 2-26; ACS Symposium Series 2003, 854, 2-9; ACS Symp. Ser. 2009, 1023, 3-13; ACS Symp. Ser. 2012, 1100, 1, and Chem. Rev. 2001, 101, 2921-2990; Progress in Polymer Science 2007, 32(1): 93-146.] These publications are incorporated by reference to provide information on the range of suitable transition metals that can participate in the redox reaction and suitable ligands for the different transition metals to form transition metal complexes suitable for polymerizing broad range of exemplified polymerizable (co)monomers. The generally accepted mechanism of an ATRP reaction is shown in Scheme 1.

ATRP is the most efficient reversible deactivation radical polymerization (RDRP) method for the preparation of pure segmented copolymers, since generally, unlike RAFT, [Moad, G.; Rizzardo, E.; Thang, S. H. Australian Journal of Chemistry 2012, 65, 985-1076.] ATRP does not require addition of a radical initiator to continuously form new polymer chains that do not contain the desired α-functional group in a grafting from/chain extension reaction and unlike NMP [Hawker, C. J.; Bosman, A. W.; Harth, E. Chemical Reviews 2001, 101, 3661-3688.] does not require high temperatures to generate the active species by thermally induced homolytic cleavage of the dormant chain end.
ATRP allows the synthesis of novel telechelic multi-segmented copolymers with one or more segments displaying a predetermined degree of polymerization, narrow molecular weight distribution (low Mw/M), incorporating a wide range of functional monomers and displaying controllable macromolecular structures under mild reaction conditions. ATRP generally requires addition or formation of an alkyl halide or (pseudo)halide as an initiator (R—X) or dormant polymer chain end (Pn-X), and a (partially) soluble transition metal complex (Cu, Fe or Ru, for example) capable of undergoing a one electron redox reaction as a catalyst.
In many cases ATRP has been implemented in non-polar solvents such as anisole, however, more polar solvents such as dimethyl sulfoxide (DMSO) and dimethyl formamide (DMF) increase the activity of an ATRP system. An interesting case is water, which is a very polar reaction medium, and dramatically increases the activity of a CuI complex in an ATRP.
Indeed an ATRP with high concentrations of CuII/L and added Cu0 in the presence of Me6TREN was first described in U.S. Pat. No. 6,541,580 as was the effect of adding polar solvents. The first aqueous ATRP was performed in 1998, and since then homogeneous and heterogeneous aqueous media have been continuously investigated since the procedures are environmentally benign, and useful for biological applications. While ATRP has been conducted in water the presence of water also presents many challenges, including the very high activity of the CuI/L complex, which can lead to a very high radical concentrations and fast radical-radical termination reactions. [Matyjaszewski et. al.; Macromol. 2009, 42, 6348-6360, Angew. Chem. 2011, 50, 11391-11394, and ACS Macro Lett. 2012, 1, 6-10.] Additional challenges in water include dissociation of the halide from the X—CuII/L deactivator complex, leading to a free halide anion and a CuII/L complex which cannot deactivate radicals, as well as decomplexation and disproportionation of the CuI/L complex. [Macromol. 2004, 37, 9768-9778 and 2012, 45, 4461-4468.]
These challenges have made conducting an aqueous Cu mediated polymerization with parts per million ((ppm), expressed as molar ratio of soluble catalyst complex to monomer not to the total volume of the reaction medium) catalyst loadings a continuing challenge.
Recent studies have demonstrated that, when the reaction is conducted in media less polar than water, concentrations of Cu as low as ca. 10 ppm can lead to well-controlled polymerizations. This was accomplished when an excess of halide salt was added to stabilize the CuII deactivator complex allowing continuous regeneration of the CuI activators and when ligands such as tris(pyridylmethyl)amine (TPMA), which form stable non-disproportionating CuI complexes, were used and the regeneration of CuI activators from CuII formed by termination events was achieved using free radical initiators in initiators for continuous activator regeneration (ICAR) ATRP, or using a reducing agent through activators regenerated by electron transfer (ARGET) ATRP, or photochemically. [Matyjaszewski, K. Et. Al. Macromol. 2012, 45, 4461-4468; Macromol. 2012, 45, 6371-6379 and ACS Macro Lett. 2012, 1, 1219-1223]
In addition recent work has also demonstrated that very well-controlled polymerizations can be conducted in water, using the Cu complexes with tris[2-(dimethylamino)ethyl]amine (Me6TREN) that is thermodynamically driven to undergo disproportionation in water. This was illustrated when a series of polymerizations were conducted in the presence of ca. 10,000 ppm of a preformed mixture of Cu0 and CuII formed by pre-polymerization disproportionation of the added CuI/Me6TREN transition metal complex in pure water. [Chem. Commun. 2013, 49, 6608-610; J. Am. Chem. Soc. 2013, 135, 7355-7363; Polym. Chem. 2014, 5(1): 57-61; and Polym. Chem. 2015 6, 406-417.] Such high levels of catalyst are undesirable in industry because of the initial cost of the added catalyst complex and the additional cost of removal of the copper catalyst from the final copolymer product. [US Patent Application, 20130197175]